1. Field of the Invention
The invention concerns anti-jack-knifing apparatus for articulated vehicles, primarily for tractor-type vehicles and articulated buses or coaches; hereafter, for simplicity, the driven and towed units of the articulated vehicle will be referred to as "tractor" and "trailer".
2. Discussion of the Prior Art
Anti-jack-knifing devices are known which exert a braking moment around a king-pin that articulates a tractor and a trailer together against the moment of forces tending to cause jack-knifing of the tractor when the tractor or the trailer is braked. Thus for instance Britsh Patent No. 1,256,947 discloses anti-jack-knifing apparatus wherein the braking moment is provided by a disc brake comprising a plurality of plates. The stationary part of the brake is fixed to the base or rubbing plate of the trailer while the rotary part is connected with the king-pin. In deviation from conventional constructions, the king-pin is not fixed rigidly to the rubbing surface of the trailer but instead has a tongue which fits into an appropriately formed part of the coupling on the tractor and thus rotates with the tractor. The plates of the brake are clamped together by a compressed-air operated piston. The air supply is taken from the air-brake system of the trailer via a special valve which operates as a function of the air pressure controlled by the foot brake valve.
In another known construction disclosed in British Patent No. 1,240,554 the anti-jack-knifing brake device is located at the steered front shaft of the trailer and is operated by a brake chamber connected into the brake system of the trailer, and this device operates simultaneously with the wheel brake of the trailer.
In a construction known from British Patent No. 1,295,045 the anti-jack-knifing device includes pistons for a disc-brake which also receive pressure from the wheel brake system of the vehicle, but only when a predetermined pressure in the brake system of the vehicle has been exceeded; this does not completely exclude the possibility of jack-knifing.
The main disadvantage of the above-mentioned known constructions is that the control of the anti-jack-knifing braking system is coupled to the operation of the braking system of the vehicle. These known control systems start from the premise that the lateral supporting force of the tyres decreases and thus the possibility of jack-knifing arises when the wheels at the rear shaft of the tractor lock on braking. However, there is not necessary logical connection between braking, locking and jack-knifing, since there can be factors other than wheel locking to cause a decrease or elimination of the lateral support forces on the tyres mounted on the rear shaft of the tractor. If jack-knifing results from a circumstance other than braking, the known anti-jack-knifing devices are ineffective.
In known devices, the anti-jack-knifing brake construction exerts a braking force the magnitude of which depends on the controlling pressure of the brake valve. In this way the upper limit of the braking effort that can be exerted is limited since the anti-jack-knifing braking construction is unable to render the articulated vehicle rigid when braking occurs during negotiating of a bend.